Is it that "CO adjustment" screw in the fuel distributor, and if so, what size and kind of tool (t-handle allen hex) fits?

If it's by fuel pressure only, does anyone use an adjustable pressure regulator in paralle with the thermo/electirc control pressure regulator?

I can break the regulator input line, attach them to a tee and bleed pressure off that, then return it to the return line at another tee.
Nylon 'air brake hose' works great for fuel lines, and can be hot-water fitted to the barbed connections.

I want to tune for gas mileage, and maybe compensate for fuel grades. It never pings. There's some scary gas out there.

"Is it that "CO adjustment" screw in the fuel distributor, and if so, what size and kind of tool (t-handle allen hex) fits?"

Yes, that is the "CO adjustment". Use a long handle 3mm hex wrench. It's a tight area for a T-handle. For extra leverage, if needed, I use a short piece of metal tubing slipped over the short leg.

Before using the 3mm wrench, get down in there with something that will pick the crud out of the 3mm set screw as much as possible. It may be stuck, and you need to get the wrench way in for a good bite.

Adjust in small increments CCW (Left) for Lean, Right for Rich, with engine warm but off, then restart. As little as 1/4 turn can make a big change sometimes. I usually back off till it stumbles, then go rich till it runs smooth. (But it's been a long time now.)

I don't know about bleeding off pressure at the CPR/WUR. Interesting theory, if you just want to go richer. Let us know how it works.


--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Now gone)
'83 Turbo 245
'73 142 (98K)
'71 144 (track modified--and still here)
New 144 from '67 to '78
Used '62 122 from '63 to '67

Thanks. 3/16 turn (left) made a difference, I think. Seems to run better and get a little better mileage, but that may be the "at least I didn't wreck it" factor. I'll let the carbon blow out for a few days and maybe readjust.
The running temperature actually dropped a little, according to the gauge.
I may need a higher thermostat.

I thought the lowering the fuel pressure would lean out the system.

The thermo/electric control pressure regulator, I thought, would keep pressure high while cold to enrich the mix. So, by bypassing the regulator and lowering the pressure below the CPR baseline, I might lean it out further. By monitoring the exhaust gas temp I should be able to tell if I'm risking valve damage. Sort of an engineering project.

Glad things improved a bit. I don't have the CPR plumbing memorized, but I know from experience that the "Control Pressure" is always LOW for a cold start (down around 20 psi in winter), then rises to about 55psi when warm (always 10-15 psi below System Pressure).

Lower control pressure on the Control Plunger allows the plunger to rise more (for a given air flow). This results in a richer mixture. The CPR doesn't really control "Fuel Pressure" at all. That is basically "fixed" by a "Line Pressure Regulator" in the Fuel Distributor.

By the way, Niel is talking about a V6 (or Turbo), with the Air Flow unit that is upside down compared to yours. Much easier to see and adjust, for sure.

--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Now gone)
'83 Turbo 245
'73 142 (98K)
'71 144 (track modified--and still here)
New 144 from '67 to '78
Used '62 122 from '63 to '67

To add something that Lucid implied, remove the hex key before starting the engine. If you don't, you can/will damage the unit. Also, it could be worth cleaning out the air flow path of the fuel metering unit. My 760 (which I've bought in a bad but running state) was extremely dirty, and I've used a whole can of carburettor cleaner to wash out the unit. Did not remove the fuel lines, just unscrewed everything and gently tipped the unit over to flush out the dirt. And there was lots of it. To check, also push down the air flow flap to feel if it moves smoothly. Also make sure that there are no air leaks on any of the inlet manifold hoses, especially ones that occur with higher vacuum, especially since you want to lean out the system. Air leaks are one of the most common K-Jet problems. I feel the hoses should have clamps fitted, as they go hard with age and start leaking. Happy tuning...